The exhaust gas discharged from the internal combustion engine in vehicles such as truck and bus, construction vehicles or the like contains particulates, which is pointed to badly exert upon environment and human body. For this end, it is demanded to develop techniques for removing the particulates from the exhaust gas. As an example of such techniques, for example, there is a ceramic honeycomb structural body for the purification of an exhaust gas using a porous ceramic member of a honeycomb structure (ceramic honeycomb structural body) for collecting and removing the particulates from the exhaust gas.
A typical example of such a ceramic honeycomb structural body, as shown in FIG. 1(b), is used as ceramic honeycomb filter 10, formed by combining a plurality of pillar-shape porous ceramic members 11 by interposing sealing material layers 14 to form a ceramic block and to form an outer periphery of the ceramic block with a sealing material layer 16 for preventing the leakage of the exhaust gas. As illustrated, the ceramic honeycomb filter 10 is constituted by bundling a plurality of ceramic members (units) 11 each having a pillar-shape honeycomb structure as one constitutional unit. In the each ceramic member 11, many cells 12 as a path for the exhaust gas are arranged in parallel to each other in longitudinal direction through cell walls 13. The particulates in the exhaust gas are removed by the cell walls 13 when the exhaust gas passes through the cell walls 13 (wall flow).
The conventional honeycomb filter for the purification of the exhaust gas has improved the exhaust gas purifying property by adjusting the size of pores (pore size) and pore size distribution in the cell wall 13. For example, JP-A-H09-313843 proposes a honeycomb structural body having such a pore structure that the pore size distribution produced in the cell wall of aluminum titanate is divided into a first region having a pore size ranging from 2 to 150 μm and a second region having a pore size ranging from 0.08 to 1 μm and each of the regions has a maximum value. The contents of JP-A-H09-313843 are incorporated therein by reference in its entirety.